The picture at right looks like New Orleans after Hurricane Katrina, but it was Elkridge, Maryland 40 years ago, after Hurricane Agnes.

Agnes did tremendous damage to the Mid-Atlantic, even though it had weakened to a tropical storm by then. At the time, it was the most costly storm ever, doing over $11 billion in damage (in 2011 dollars). It also killed 128 people.

In Florida, Agnes spawned 28 tornadoes. In DC, it flooded the National Zoo, and the Potomac River rose 15½ feet next to Georgetown. It also caused the greatest flooding ever recorded in Maryland, with bridges washed out in Laurel, and Ellicott City under as much as 14½ feet of water. The entire state of Pennsylvania was declared a disaster area.